The split, largely generational given the youthful tilt of the Vermont senator’s supporters, underscored a hard truth for California Democrats that was barely discussed during the celebratory convention:

Numbers-wise, the party's heading for trouble.

That’s not to suggest that Democrats are about to lose elections in California; they retain strength at the ballot box. But as those who built the party into supremacy in the 1990s age out, Democrats are having a hard time attracting newer voters, who are allying themselves with no party at all. They are choosing, if they register, to officially be nonpartisan.

For now, the effect on Democrats has been limited because those independent voters, bridling at the conservative views of national Republicans, have had nowhere to go but with the state’s biggest party.

“Whether you want to say ‘Madame President’ or whether you are ‘Feeling the Bern’ we have to stand together,” she said. Applause for Hillary Clinton, the party’s national and statewide frontrunner, was drowned out by cheers for Sanders.

And that was among committed Democrats. Broaden the universe of voters and the problems get worse.

The birth of the current California Democratic Party dates to 1992, when the state elected two Democratic women senators, Dianne Feinstein and Boxer, who has announced her retirement as of the November election. California also sided with a Democrat, Bill Clinton, in that year’s presidential contest, breaking a Republican streak that had held since 1964. Republicans went on to win the governor’s race in 1994, but it’s been downhill since, with the exception of Arnold Schwarzenegger’s two elections.

At a Saturday convention panel focused on millennial voters — roughly those 35 and under — voting analyst Paul Mitchell issued a warning to Democrats.

“Republicans are dying,” he said. “But Democrats aren’t converting ... young minority voters who are the base of the Democratic Party.”

Of the 10 cities with the highest percentages of independent voters, he said, all but one are Latino-majority cities. That is jarring, since Democratic strength in the last generation has been built on the growing Latino population.

Eric Swalwell, 35, the East Bay congressman who organized the panel, said the strong support for Sanders in the presidential contest was a warning to the party’s older establishment.

“Regardless of whether you’re with Bernie Sanders or Hillary Clinton, there’s no question that right how Bernie Sanders has the overwhelming majority of the millennials,” said Swalwell, who endorsed Clinton after his first choice, former Maryland Gov. Martin O’Malley, dropped out. “Whoever is the candidate, as a party we have to understand why that is the case.”

Why that’s the case is the candidates themselves. To young voters for whom she has been a life-long presence, Clinton looks like a captive of establishment politics. Sanders, with his call to “political revolution,” is the blunt-speaking fresh face.

“Authenticity is so, so important for millennials,” Swalwell said. “Being able to really just speak without being seen as beholden to anyone is critically important.”

Democrats have emphasized issues of importance to younger voters. Sanders and Clinton have offered differing proposals making college less expensive or, in Sanders’ case, free. Their focus on lagging wages, immigration reform and voting rights is also aimed at the new voters who have less affinity with partisan politics.

The Republican candidates for president are delaying the reckoning for Democrats. At the weekend convention, nearly every speaker blistered Donald Trump and other GOP candidates as hopelessly out of touch.

The Republican field’s effort to turn back the clock on Democratic gains under President Obama has left both parties waging the wars of the past in this presidential year.

Change is coming to California Democrats. The next governor, to be elected in 2018, will most certainly be younger than 77-year-old Jerry Brown. The main competitors for the 75-year-old Boxer’s seat are in their 50s. If Feinstein, who is now 82, retires in 2018, her replacement also will be younger.

Age is not an impediment to attracting the young, as Sanders, at 74, has proved this year. But new faces and a look to the future may give Democrats a way to figure out how to preserve their power.